[llvm-dev] LLVM Developers Meeting JIT BoF -- Request for Topics of Interest

[Lang Hames via llvm-dev]

Hi Geoff,

I have only encountered one problem. If a static library has not been
> compiled with -fPIC and uses symbols from a shared library, LLJIT does not
> complain, but the code may crash without warning when it is executed.


Was the static library compiled with large code model too?

I think this is probably a RuntimeDyld bug: It's not great at error
reporting. A few people in the community are working on an ELF/x86-64
implementation of JITLink at the moment -- Once we have that you should get
small code model support and better error handling.

-- Lang.

On Fri, Oct 2, 2020 at 4:03 AM Geoff Levner <glevner at gmail.com> wrote:

> StaticLibraryDefinitionGenerator works as promised on ELF archives!
>
> I have only encountered one problem. If a static library has not been
> compiled with -fPIC and uses symbols from a shared library, LLJIT does not
> complain, but the code may crash without warning when it is executed.
>
> Geoff
>
> On Mon, Sep 28, 2020 at 11:58 PM Lang Hames <lhames at gmail.com> wrote:
>
>> Hi Geoff,
>>
>> We use LLJIT. Do addObjectFile() and StaticLibraryDefinitionGenerator
>>> work for ELF objects?
>>
>>
>> They do. :)
>>
>> I've not tested StaticLibraryDefinitionGenerator extensively on Linux.
>> but we have a regression test checking basic usage. If you run into any
>> trouble at all please file a bug and assign it to me.
>>
>> -- Lang.
>>
>>
>>
>> On Mon, Sep 28, 2020 at 2:05 PM Geoff Levner <glevner at gmail.com> wrote:
>>
>>> We use LLJIT. Do addObjectFile() and StaticLibraryDefinitionGenerator
>>> work for ELF objects?
>>>
>>> On Mon, Sep 28, 2020 at 10:57 PM Lang Hames <lhames at gmail.com> wrote:
>>> >
>>> > Hi Geoff,
>>> >
>>> >> Importing symbols into the JIT from an object file or static
>>> library...?
>>> >
>>> >
>>> > Sure! Are you interested in doing this with the C API, LLJIT, or raw
>>> OrcV2 components?
>>> >
>>> > The high-level answer here (which we can dig into further in the BoF)
>>> is:
>>> >
>>> > For object files:
>>> > - For raw OrcV2 components you'll want to create an
>>> RTDyldObjectLinkingLayer or ObjectLinkingLayer and use the 'add' method.
>>> > - For an LLJIT instance you can just call the 'addObjectFile' method.
>>> > - For the OrcV2 C API you can call the 'LLVMOrcLLJITAddObjectFile'
>>> function.
>>> >
>>> > For static libraries:
>>> > - For raw OrcV2 components or an LLJIT instance you can attach a
>>> StaticLibraryDefinitionGenerator [1] to the JITDylib that you would like to
>>> load the library into. See [2] for an example.
>>> > - For the OrcV2 C API we will just need to add a method to wrap the
>>> operation above. We already have
>>> 'LLVMOrcCreateDynamicLibrarySearchGeneratorForProcess'. We should add
>>> counterparts to that to load dynamic and static libraries from paths.
>>> >
>>> > -- Lang.
>>> >
>>> > [1]
>>> https://github.com/llvm/llvm-project/blob/5aa56b242951ab0f0181386ea58509f19b09206e/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h#L361
>>> > [2]
>>> https://github.com/llvm/llvm-project/blob/e7549dafcd33ced4280a81ca1d1ee4cc78ed253f/llvm/tools/lli/lli.cpp#L968
>>> >
>>> >
>>> > On Mon, Sep 28, 2020 at 7:18 AM Geoff Levner <glevner at gmail.com>
>>> wrote:
>>> >>
>>> >> Importing symbols into the JIT from an object file or static
>>> library...?
>>> >>
>>> >> On Mon, Sep 28, 2020 at 5:29 AM Lang Hames <lhames at gmail.com> wrote:
>>> >>>
>>> >>> Hi Andres,
>>> >>>
>>> >>>> A topic that I'd find interesting is what it'd take to make it
>>> easier to
>>> >>>> use profile guided optimization in the context of JIT.  A few years
>>> back
>>> >>>> I crudely hacked this together, but it was fairly ugly. It'd be
>>> nice to
>>> >>>> make that easier.  Possibly too complicated for that type of
>>> session?
>>> >>>
>>> >>>
>>> >>> We couldn't go into detail, but we could kick off a discussion and
>>> identify who is interested in working on this. My pitch: We should solve
>>> this by investing in JITLink and implementing profiling (and debugger
>>> support) via ObjectLinkingLayer::Plugins. Maybe a brief overview of /
>>> discussion on how these work would be useful?
>>> >>>
>>> >>> -- Lang.
>>> >>>
>>> >>>
>>> >>> On Fri, Sep 25, 2020 at 7:19 PM Andres Freund <andres at anarazel.de>
>>> wrote:
>>> >>>>
>>> >>>> Hi,
>>> >>>>
>>> >>>> On 2020-09-25 19:05:42 -0700, Lang Hames wrote:
>>> >>>> > The 2020 Virtual LLVM Developer's Meeting is coming up the week
>>> after next.
>>> >>>> > I'll be hosting a JIT Birds-of-a-Feather session on Thursday the
>>> 8th at
>>> >>>> > 10:55am PDT (See http://llvm.org/devmtg/2020-09/schedule/). I'm
>>> planning to
>>> >>>> > run this more like a Round Table: Minimal introduction, plenty of
>>> time for
>>> >>>> > discussion.
>>> >>>> >
>>> >>>> > Does anyone have any LLVM JIT related topics that they would
>>> particularly
>>> >>>> > like to discuss at this session? Any questions that they think
>>> could be
>>> >>>> > best answered by a round-table style discussion? I'll aim to rope
>>> in the
>>> >>>> > right people and prepare answers to make sure we get the most out
>>> of the
>>> >>>> > session.
>>> >>>>
>>> >>>> A topic that I'd find interesting is what it'd take to make it
>>> easier to
>>> >>>> use profile guided optimization in the context of JIT.  A few years
>>> back
>>> >>>> I crudely hacked this together, but it was fairly ugly. It'd be
>>> nice to
>>> >>>> make that easier.  Possibly too complicated for that type of
>>> session?
>>> >>>>
>>> >>>> I dimly recall that the main issue was that there is no good way to
>>> >>>> extract the profile information without going through files /
>>> applying
>>> >>>> the profile data without going through files.
>>> >>>>
>>> >>>> Greetings,
>>> >>>>
>>> >>>> Andres Freund
>>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20201002/6cf932ca/attachment.html>